Four-cycle internal combustion engines typically Lise at least two valves per cylinder, one being an intake valve and the other an exhaust valve. Many of these engines even use three or more valves per cylinder. For example., some engines include two intake valves and two exhaust valves per cylinder. The valves of an internal combustion engine are operated by a valve actuating mechanism that typically is either a pushrod or an overhead camshaft valve train. The valve actuating mechanism translates rotating motion from the rotating camshaft of the engine into reciprocal linear motion of the individual valves.
The multiplicity of moving parts, the mass, and the high energies and revolutions involved in modern combustion engines often result in not only significant amounts of undesired vibration and noise, but can also result in decreased engine speed and efficiency. It has long been recognized that improvements to the valve train components can lead to significant improvements in overall engine performance. More particularly, valves of reduced weight offer the potential to lower engine noise, increase engine speed, increase engine power, and improve fuel efficiency.
In one approach for reducing the weight of valves, valves have been formed from titanium alloys, which generally are characterized by a combination of lightweight, high strength, temperature resistance, and corrosion resistance. Valves made from titanium alloys have been described, for example, in U.S. Pat. Nos. 5,112,415 (Mae); 5,370,092 (Shimizu et al.); and 4,729,546 (Allison).
In another approach, valves formed from composites have been described. For example, U.S. Pat. No. 4,928,645 (Berneburg et al.) describes a ceramic composite valve whose valve stem includes a fibrous ceramic sleeving packed with axially aligned fibers. U.S. Pat. No. 4,852,531 (Abkowitz) describes a valve whose composite valve stem includes a titanium alloy strengthened with particles of TiC, TiB, or TiB.sub.2.
The two approaches described above involve the use of solid valve stems. In a further effort to reduce weight, hollow valve stems have also been proposed. For example, U.S. Pat. No. 4,834,036 (Nishiyama et al.) describes a valve with a hollow valve stem formed from a high strength alloy steel. The high strength of such steel makes a hollow valve stem technically feasible. However, even with a hollow stem, such valves are still relatively heavy.
There still remains a need, therefore, for lighter weight valves to further improve the efficiency, performance, and power output of internal combustion engines. Specifically, lighter weight valves would offer potential for higher attainable engine rpm, more attainable horsepower, longer service life, less engine noise, and better fuel economy.